Fully embedded nanoparticles do not migrate

Scientists review experimental and modeling studies on migration of nanoparticles from food contact plastics; conclude that no migration will occur if nanoparticles are fully embedded in polymer; mechanical stress or damage could lead to increased release

March 3, 2017 Ksenia Groh

An article published on February 27, 2017 in the peer-reviewed journal Trends in Food Science & Technology provides a critical account of experimental and modeling studies dealing with potential migration of nanoparticles from food contact plastics into food or food simulants. Angela Stoermer and colleagues from Fraunhofer Institute for Process Engineering and Packaging IVV, Freising, Germany, reviewed over 20 published studies and found that most of them dealt with silver nanoparticles. This could be either because of a high number of potential applications of this nanomaterial, or just because total silver can be relatively easily and sensitively measured in food simulants or food, the authors argue.

The authors further emphasized that silver nanoparticles may not be the best choice of model nanoparticles with which to perform research on the important question of whether nanoparticles do or do not migrate from food contact plastics. This is because of the lack of fully reliable methods to measure nanoparticulate silver, and also because there is a high potential for experimental artefacts in studies with silver. Incorrect conclusions on the migration of silver in nanoform may be reached because silver ions can be easily reduced back to elemental silver, resulting in a ‘re-growth’ of nanoparticles in the solution after initial migration of ionic species.

Migration studies which worked with nanoparticles other than silver (or copper, another soluble metal), i.e. studies using “inert, insoluble and non-redox friendly” nanomaterials such as titanium nitride or carbon black, came to the conclusion that no migration of nanoparticles from food contact plastics occurs. The authors further summarized the mathematical modeling studies which extended recognized migration models to nanoparticles, considering them as quasi-molecules of a certain molecular volume. These studies found that, if Fickian diffusion is considered as the main mechanism, then “only nanoparticles up to 3 or 4 nm, and only if present in polymers like polyolefins, could give rise for measurable migration.” Nanoparticles normally used in food contact plastics are at least several times larger than that.

The above considerations are applicable only to nanoparticles which are fully embedded, i.e. “covered or encapsulated by the host polymer,” with no direct contact of nanoparticles with food or food simulant. In such a situation, nanoparticles “do not have a potential to penetrate . . . outer layer and do not migrate into food.” However, nanoparticle release may still occur “in case of mechanical impact on the food contact surface which would alter the smooth properties or, in case of cut edges or otherwise technically improperly manufactured PNCs [(polymer nanocomposites)] with nanoparticles sticking out of the surface.”

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